A hornless bull is crossed with three cows, A, B, and C. Cow A is horned and produces calf A', which is also horned. Cow B is hornless and produces calf B', which is horned. Cow C is horned and produces calf C', which is hornless. Which is the dominant trait? Explain your reasoning. Give the genotypes of all seven animals.

The dominant trait is hornless.

If this is correct, then the original bull is a heterozygote:

H = hornless

h = horned

Bull is Hh

Cross 1: Hh x hh (horned female) - offspring is hh (horned)

Cross 2: Hh x Hh (hornless female) - offspring is hh (horned)

Cross 3: Hh x hh (horned female) - offspring is Hh (hornless)

Cross 3 is the key to confirming this because the only way to get a hornless offspring would be if hornless is recessive.